Why would you want to put ash in pots? Most papers these days have all sorts of chemical fillers that may or may not harm your plants in such a closed space, so why chance it. If you can see the individual fibres in the paper when you look at it closely then it may be mostly cellulose, i.e. plant fibres, but if it is glossy and shiny like plastic sheet then it is heavily coated or treated with fillers or resins. You can always shred it manually or mechanically, and put it on your compost heap or your green waste bin, where the dilution will minimise any chemical effects.
